Non-magnetic austenitic stainless steel having excellent corrosion resistance and manufacturing method therefor

ABSTRACT

Disclosed is a non-magnetic austenitic stainless steel with excellent corrosion resistance which is applicable to an environment requiring corrosion resistance along with excellent non-magnetic properties, and manufacturing method thereof. The non-magnetic austenitic stainless steel with excellent corrosion resistance according to an embodiment of the present disclosure includes, in percent (%) by weight of the entire composition, C: 0.05% or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% or less, the remainder of iron (Fe) and other inevitable impurities, and satisfies a following equation (1). 
       Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)

TECHNICAL FIELD

The present disclosure relates to a non-magnetic austenitic stainlesssteel, and more particularly, to a non-magnetic austenitic stainlesssteel with excellent corrosion resistance applicable to an environmentrequiring corrosion resistance together with non-magnetic properties,and a manufacturing method thereof.

BACKGROUND ART

Austenitic stainless steel, represented by STS304, has good corrosionresistance, and exhibits a non-magnetic austenite structure in annealingheat treatment, and is used as a non-magnetic steel in various devices.However, there are cases where cold working is performed depending onthe application, and when cold working is applied to STS304 steel, dueto the phase transformation to deformation induced martensite structure,it is difficult to maintain non-magnetic properties, which limits theapplication to materials.

Therefore, STS316L-based steel grades with higher austenite stabilitythan STS304 are used for non-magnetic applications. However, in the caseof STS316L-based steel grades, the Mo content is high, so a secondaryphase such as σ or δ-ferrite is often present in the austenite matrix,and since the solidification starts from δ-ferrite during continuouscasting of STS316L steel, it is difficult to decompose the secondaryphases due to high Cr and Mo content in the center segregation region inthe continuous casting slab, and thus the secondary phases tend toremain after hot rolling and final heat treatment.

When the secondary phases remain, it acts as a cause of increasedmagnetism in the area, and adversely affects the function of the device.Therefore, there is a need for a material capable of maintainingnon-magnetic properties without these secondary phases.

Patent Document 1 refers to a high-strength non-magnetic austeniticstainless steel that maintains non-magnetic properties even after severecold working and can significantly improve elastic limit stress by agingtreatment.

However, the stainless steel of Patent Document 1 has a Mn content of 2to 9%, so it is feared that corrosion resistance is reduced due to Mn,and its application is limited in applications requiring corrosionresistance. For the stabilization of the austenite phase, Ni-equivalentrange was proposed to refer to maintaining non-magnetic properties evenafter cold working. However, since δ-ferrite, which affects non-magneticproperties, is not mentioned, it is necessary to solve the deteriorationof non-magnetic properties due to δ-ferrite formation.

(Patent Document 0001) Korean Patent Publication No. 10-2015-0121061(Oct. 28, 2015)

DISCLOSURE Technical Problem

Therefore, it is an aspect of the present invention to provide a highlycorrosion-resistant austenitic stainless steel with excellentnon-magnetic properties by suppressing δ-ferrite formation duringsolidification by solving the above problems.

Technical Solution

In accordance with an aspect of the present disclosure, a non-magneticaustenitic stainless steel with excellent corrosion resistance includes,in percent (%) by weight of the entire composition, C: 0.05% or less,Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2%or less, the remainder of iron (Fe) and other inevitable impurities, andsatisfies a following equation (1), and has a permeability of 1.02μ orless.

Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)

Ni, C, Si, Mn, Cr, Mo, Cu, N mean the content (% by weight) of eachelement.

The austenitic stainless steel may further include: in percent (%) byweight, Cu: 3.0% or less.

The austenitic stainless steel may further include: in percent (%) byweight, Mo: 4.0% or less.

The austenitic stainless steel may further include: in percent (%) byweight, B: less than 0.01%.

The austenitic stainless steel may satisfy a calculated δ-ferritefraction represented by the following equation (2) of 0% or less.

161*{[Cr+Mo+1.5*Si+18]/[Ni+30*(C+N)+0.5*(Cu+Mn)+36]+0.262}−161  (2)

Cr, Mo, Si, Ni, C, N, Cu, Mn mean the content (% by weight) of eachelement The austenitic stainless steel may satisfy a pitting resistanceequivalent number (PREN) represented by the following equation (3) ofthe range of 20 to 30.

Cr+3.3*Mo+30*N−Mn+Si  (3)

Cr, Mo, N, Mn, Si mean the content (% by weight) of each element Theaustenitic stainless steel may satisfy a σ phase formation indexrepresented by the following equation (4) of the range of 18 to 24.

Cr+Mo+3*Si  (4)

Cr, Mo, Si mean the content (% by weight) of each element

The austenitic stainless may have a permeability of 1.012μ or less.

The average grain size of the stainless steel may be 70 μm or less.

In accordance with an aspect of the present disclosure, a manufacturingmethod of a non-magnetic austenitic stainless steel with excellentcorrosion resistance, includes: hot rolling the slab comprising, inpercent (%) by weight of the entire composition, C: 0.05% or less, Si:1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% orless, the remainder of iron (Fe) and other inevitable impurities andsatisfying a σ phase formation index represented by the followingequation (4) of the range of 18 to 24; and performing a solution heattreatment of the hot rolled material.

(4) Cr+Mo+3*Si Cr, Mo, Si mean the content (% by weight) of each elementThe slab may satisfy a following equation (1), and satisfy a calculatedδ-ferrite fraction represented by a following equation (2) of 0% orless.

Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)

161*{[Cr+Mo+1.5*Si+18]/[Ni+30*(C+N)+0.5*(Cu+Mn)+36]+0.262}161  (2)

The solution heat treatment may be performed at 1,100 to 1,150° C. for60 to 120 seconds.

Advantageous Effects

High corrosion-resistant non-magnetic austenitic stainless steelaccording to an embodiment of the present disclosure can be applied to avariety of non-magnetic components used in various devices.

In addition, since the non-magnetic property is determined by thecomponents without an additional process of heat-treating the materialfor a long time in order to remove the magnetism by δ-ferrite, it ispossible to provide non-magnetic austenitic stainless steel with asimple manufacturing process.

In addition, it is possible to prevent roughness deterioration due to anorange peel defect on the surface of the steel sheet.

DESCRIPTION OF DRAWINGS

FIG. 1 is a graph illustrating a correlation of permeability accordingto a difference between a Ni content and a Ni correction value(Ni_(adj)).

BEST MODE

A non-magnetic austenitic stainless steel with excellent corrosionresistance according to an embodiment of the present disclosureincludes, in percent (%) by weight of the entire composition, C: 0.05%or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to16%, N: 0.2% or less, the remainder of iron (Fe) and other inevitableimpurities, and satisfies a following equation (1), and has apermeability of 1.02μ or less.

Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)

Ni, C, Si, Mn, Cr, Mo, Cu, N mean the content (% by weight) of eachelement.

MODES OF THE INVENTION

Hereinafter, the embodiments of the present disclosure will be describedin detail with reference to the accompanying drawings. The followingembodiments are provided to transfer the technical concepts of thepresent disclosure to one of ordinary skill in the art. However, thepresent disclosure is not limited to these embodiments, and may beembodied in another form. In the drawings, parts that are irrelevant tothe descriptions may be not shown in order to clarify the presentdisclosure, and also, for easy understanding, the sizes of componentsare more or less exaggeratedly shown.

Also, when a part “includes” or “comprises” an element, unless there isa particular description contrary thereto, the part may further includeother elements, not excluding the other elements.

An expression used in the singular encompasses the expression of theplural, unless it has a clearly different meaning in the context.

Hereinafter, it describes a non-magnetic austenitic stainless steelwhich can secure non-magnetic properties even if it is manufactured in anormal process without requiring an additional process for decomposingδ-ferrite by controlling the content of δ-ferrite present in themicrostructure of the steel and has superior corrosion resistancecompared to commonly used STS316L stainless steel.

The present disclosure provides austenitic stainless steel whichexhibits excellent non-magnetic properties only by controlling the alloyelement components even without an additional heat treatment process,and a manufacturing method thereof.

A non-magnetic austenitic stainless steel with excellent corrosionresistance according to an embodiment of the present disclosureincludes, in percent (%) by weight of the entire composition, C: 0.05%or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to16%, N: 0.2% or less, the remainder of iron (Fe) and other inevitableimpurities, and satisfies a following equation (1).

Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)

Hereinafter, the reason for the numerical limitation of the alloycomponent element content in the embodiment of the present disclosurewill be described. In the following, unless otherwise specified, theunit is % by weight.

The content of C is 0.05% or less.

C is a strong austenite phase stabilizing element and is an effectiveelement for increasing material strength by solid solutionstrengthening. However, when the content is excessive, it is easilycombined with a carbide-forming element such as Cr effective forcorrosion resistance at the ferrite-austenite phase boundary, therebylowering the Cr content around the grain boundaries to reduce corrosionresistance. Therefore, the content of C is limited to 0.05% or less. Inorder to minimize the risk of carbide precipitation, which can inhibitcorrosion resistance, it is desirable to limit the content of C to 0.03%or less.

The content of Si is 1.0% or less.

Si, which also acts as a ferrite phase stabilizing element, is effectivein improving corrosion resistance, but when it is excessive, it promotesprecipitation of intermetallic compounds such as σ phase, therebyreducing mechanical properties and corrosion resistance related toimpact toughness, and is limited to 1.0% or less.

The content of Mn is 0.5 to 2.0%.

Mn is an austenite phase stabilizing element such as C and Ni, which canimprove the N solubility, and is added by 0.5% or more. However, anincrease in the Mn content is undesirable when corrosion resistance isrequired because it is involved in the formation of inclusions such asMnS, so it is preferable to limit the Mn content to 2.0% or less inorder to secure corrosion resistance.

The content of Cr is 16.0 to 24.0%.

Cr is the most contained element of the corrosion resistance enhancingelement of stainless steel, and must be included by 16% or more for theexpression of corrosion resistance. However, Cr is a ferrite stabilizingelement. As the Cr content increases, the ferrite fraction increases.Therefore, in order to obtain a non-magnetic property, since a largeamount of Ni must be contained, the cost increases, and the formation ofthe σ phase is promoted, causing a decrease in mechanical properties andcorrosion resistance. Therefore, it is preferable to limit the Crcontent to 24% or less.

The content of Ni is 10.0 to 16.0%.

Ni is the most powerful element of the austenite phase stabilizingelement and must be contained by 10% or more to obtain non-magneticproperties. However, since the increase in Ni content is directlyrelated to the increase in the price of raw materials, it is preferableto limit Ni content to 16% or less.

The content of N is 0.2% or less.

N is an element useful for stabilizing the austenite phase as well asimproving corrosion resistance in a chlorine atmosphere. However, it ispreferable to limit N content to 0.2% or less, because the hotworkability is reduced when a large amount is added to lower theyielding percentage of steel.

In addition, according to an embodiment of the present disclosure, byweight %, Cu of 3.0% or less may be further included.

Cu has the advantage of improving corrosion resistance in a sulfuricacid atmosphere, so it can be selectively added. However, in thechlorine atmosphere, there is a disadvantage of reducing the pittingresistance and lowering the hot workability, so it is limited to 3.0% orless.

In addition, according to an embodiment of the present disclosure, byweight %, Mo of 4.0% or less may be further included.

The content of Mo is 4.0% or less.

Mo is an element useful for improving corrosion resistance, and can beexpected to improve corrosion resistance, so it can be selectivelyadded. When adding, it is preferable to add 2.0% or more. However, Mo isa ferrite stabilizing element, and when added in large amounts, it isdifficult to obtain a non-magnetic property due to an increase in theferrite fraction and, in addition, the formation of the σ phase ispromoted, leading to a decrease in mechanical properties and corrosionresistance. Therefore, the content of Mo is limited to 4.0% or less.

In addition, according to an embodiment of the present disclosure, byweight %, B may be further included less than 0.01%.

The content of B is less than 0.01%.

B has the effect of improving the hot workability, so it can be added ina range of less than 0.01%. However, when it is added more than that,since a low melting point boride compound is formed and rather hotworkability is lowered, it is preferable to limit to less than 0.01%.

In various devices that use non-magnetic properties of steel, thepermeability of the steel applied to the parts must be 1.02μ or less fornormal device operation. In order to satisfy this, it is necessary tocontrol the fraction of δ-ferrite formed during solidification of thesteel.

In general, δ-ferrite present in the microstructure of austeniticstainless steel becomes magnetic due to the characteristics of thestructure having a body-centered cubic structure, and austenite does notbecome magnetic due to the face-centered cubic structure. Therefore, itis possible to obtain a magnetic property of a desired size bycontrolling the fraction of δ-ferrite, and in the case of non-magneticsteel, it is necessary to make the fraction of δ-ferrite as low aspossible or eliminate the fraction of δ-ferrite.

The fraction of δ-ferrite present in the microstructure of austeniticstainless steel can be determined by the content of various alloyingelements, as shown in equation (2), which will be described later. Inparticular, it is possible to reduce the δ-ferrite fraction by adding anaustenite stabilizing element. Since the Ni content is useful forstabilizing austenite without deteriorating other physical properties,the Ni content can be controlled to suppress the formation of δ-ferrite.

The Ni correction formula (hereinafter, Ni_(adj)) means a minimum Nicontent that prevents δ-ferrite from being formed in a given compositioncomponent, and can be expressed as follows.

−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  [Ni_(adj)]

When the Ni content contained in the actual steel is greater than thevalue of Ni_(adj), δ-ferrite cannot be formed, thereby exhibitingnon-magnetic properties. That is, in order to satisfy the non-magneticproperty, it means that the content of Ni contained in the steel shouldbe greater than Ni_(adj) combined with the content of C, Si, Mn, Cr, Mo,Cu, and N components.

Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)

FIG. 1 is a graph illustrating a correlation of permeability accordingto a difference between a Ni content and a Ni_(adj) value. Referring toFIG. 1, it can be seen that when the difference between the Ni contentand the Ni_(adj) value included in the steel is positive, thepermeability of the steel satisfies 1.02μ or less.

However, Ni is an expensive alloy element, and the more Ni is added, thehigher the cost. Therefore, it is preferable to make the differencebetween the actual Ni content and the Ni_(adj) value less than 8%.

In addition, according to an embodiment of the present disclosure, thenon-magnetic austenitic stainless steel with excellent corrosionresistance may satisfy the calculated δ-ferrite fraction represented bythe following equation (2) of 0% or less.

161*{[Cr+Mo+1.5*Si+18]/[Ni+30*(C+N)+0.5*(Cu+Mn)+36]+0.262}−161  (2)

The equation (2) is a formula that can predict the δ-ferrite content ofsteel through the content of each component when producing austeniticstainless steel in a normal steelmaking process. When the fraction ofδ-ferrite calculated through equation (2) is 0% or less, thenon-magnetic property to be achieved in the present disclosure may besatisfied.

The non-magnetic austenitic stainless steel of the present disclosureaccording to the equations (1) and/or (2) may exhibit a permeability of1.02μ or less, and more preferably 1.012μ or less, thereby realizing acompletely non-magnetic property.

On the other hand, in order to improve corrosion resistance of steel, itis effective to add alloy elements that improve corrosion resistance,such as Cr, Mo, Si, and N. In addition, when a large amount of Mn isadded, since water-soluble inclusions such as MnS in steel are formedand corrosion resistance is lowered, it is necessary to control the Mncontent.

In general, as an index indicating corrosion resistance of austenitestainless steel, pitting resistance equivalent number calculated by acombination of Cr, Mo, and N contents is applied. However, as describedabove, since the contents of Mn and Si also greatly affect corrosionresistance of steel, a new pitting resistance equivalent numberconsidering these elements is also required.

According to an embodiment of the present disclosure, non-magneticaustenitic stainless steel with excellent corrosion resistance maysatisfy a pitting resistance equivalent number (PREN) value representedby the following equation (3) of the range of 20 to 30.

Cr+3.3*Mo+30*N−Mn+Si  (3)

The present inventors have found that the pitting resistance equivalentnumber including Mn and Si content represented by equation (3) wellreflects the corrosion resistance of steel, and have confirmed that whenthe range of equation (3) is 20 to 30, corrosion resistance may be equalto or higher than that of conventional STS316L.

However, when the content of Cr, Mo, and Si increases, not only does thecost increase, but the formation of the σ phase promotes brittleness,and a Cr and Mo depletion region is formed, which adversely affectscorrosion resistance. Therefore, it is necessary to set an appropriateCr, Mo, Si content range that can minimize the formation of the σ phasewhile obtaining desired corrosion resistance.

According to an embodiment of the present disclosure, the non-magneticaustenitic stainless steel with excellent corrosion resistance maysatisfy the σ phase formation index represented by the followingequation (4) of the range of 18 to 24.

Cr+Mo+3*Si  (4)

When the σ phase formation index is less than 18, the Cr and Mo contentis so low that it is difficult to secure corrosion resistance of thesteel, so it is limited to 18 or more.

By limiting the σ phase formation index to 24 or less, the σ phasefraction can be controlled to less than 1.0%, more preferably to 0.8% orless. When the σ phase formation index is greater than 24, decreasedcorrosion resistance and brittle material degradation due to excessive σphase formation may occur. Non-magnetic properties may be furtherimproved by securing a low σ phase fraction.

On the other hand, the σ phase formation control can suppress theformation of the σ phase by controlling the alloy component compositionas in the present disclosure, but the formed σ phase may also bedecomposed by controlling the solution heat treatment conditions. Forthe decomposition of the σ phase, it is effective to anneal for a longtime at a high temperature, but in this case, the possibility of causingan orange peel defect on the surface increases due to excessive grainsize growth. Here, the orange peel defect refers to a defect in whichunevenness of roughness occurs on the surface when the steel is formedby coarse grain size, thereby damaging the beautiful surface.

According to an embodiment of the present disclosure, the average grainsize of non-magnetic austenitic stainless steel with excellent corrosionresistance may be 70 μm or less.

For general 300-based austenitic stainless steel, solution heattreatment is performed at about 1,100° C. for about 60 to 100 seconds.In order to lower the incidence of defects in orange peel duringmolding, the average grain size of stainless steel should be 70 μm orless, and for this purpose, the average grain size of the non-magneticaustenitic stainless steel with excellent corrosion resistance of thepresent disclosure may be controlled to 70 μm or less by performingsolution heat treatment of the hot rolled material at 1,100 to 1,150° C.for 60 to 120 seconds.

Hereinafter, it will be described in more detail through a preferredembodiment of the present disclosure.

Example

After the steel having the alloy composition shown in Table 1 wasdissolved in a vacuum induction furnace, hot rolling was performed, andsolution heat treatment was performed to prepare a hot rolled sheethaving a thickness of 6 mm.

TABLE 1 composition (wt %) C Si Mn Cr Ni Mo Cu N B S1 0.030 0.45 1.315.8 15.8 0.0 1.5 0.070 0.0026 S2 0.034 0.46 1.2 18.5 15.4 0.0 1.2 0.0800.0045 S3 0.025 0.52 1.2 20.4 16.0 0.0 1.3 0.080 0.0035 S4 0.028 0.471.4 24.3 15.4 0.0 1.6 0.070 0.0026 S5 0.021 0.45 1.3 18.6 14.3 0.0 2.10.090 0.0025 S6 0.024 0.46 1.1 17.9 14.5 2.8 0.0 0.080 0.0025 S7 0.0260.43 1.2 17.6 10.5 0.0 2.5 0.120 0.0026 S8 0.030 0.42 1.2 18.6 13.5 4.22.6 0.090 0.0034 S9 0.037 0.48 1.3 18.1 12.6 2.1 1.5 0.220 0.003 S100.032 0.45 1.3 18.2 13.5 2.5 1.6 0.100 0.002 S11 0.026 0.45 1.2 17.914.2 2.6 1.4 0.050 0.0021 S12 0.028 0.46 0.5 18.1 13.8 0.0 0.0 0.0700.0026 S13 0.029 0.47 1.3 18.4 13.9 0.0 0.6 0.080 0.0026 S14 0.027 0.412.2 18.1 13.9 0.0 0.0 0.080 0.0032 S15 0.024 0.42 1.2 18.1 14.5 2.1 0.30.080 0.0025 S16 0.026 0.75 1.3 18.4 14.0 2.0 0.4 0.090 0.003 S17 0.0351.12 1.1 18.7 13.9 2.3 0.6 0.110 0.0026

In some of the S1 to S17 steel types listed in Table 1, the solutionheat treatment conditions were varied to change the grain size, and whenthe steel with each grain size was formed, the incidence of orange peeldefects was investigated and shown in Table 2 below.

TABLE 2 orange average peel solution heat treatment grain incidencetemperature(° C.) time(sec) size(μm) (%) Inventive 1 S2 1,150 90 23.48<1.0 Example 2 S3 1,150 90 30.45 <1.0 3 S5 1,150 90 25.63 <1.0 4 1,10090 22.89 <1.0 5 1,150 180 50.88 3.2 6 1,180 90 53.48 3.5 7 S6 1,150 9030.89 <1.0 8 S7 1,150 90 38.52 <1.0 9 S10 1,150 90 23.58 <1.0 10 S111,150 90 25.25 <1.0 11 S12 1,150 90 26.84 <1.0 12 S13 1,150 90 21.35<1.0 Comparative 13 S1 1,150 90 21.93 <1.0 Example 14 S4 1,150 90 27.56<1.0 15 S5 1,180 120 74.58 15.8 16 1,180 180 86.72 22.9 17 S8 1,150 9024.69 <1.0 18 S9 1,150 90 23.75 <1.0 19 S14 1,150 90 26.84 <1.0 20 S171,150 90 31.24 <1.0

As shown in Table 2, the S5 steel grades used in Comparative Examples 15and 16 satisfy all the components of the present disclosure, but thesolution heat treatment temperature was performed at 1,180° C. exceeding1,150° C. for 120 seconds or more and the average grain size exceeded 70μm, and the orange peel defect after molding was more than 15%.

As the solution heat treatment temperature changed, the grain size ofthe steel changed. As the heat treatment temperature and time increased,it was found that the average grain size increased. When the averagegrain size was 70 μm or more, it was found that the incidence of orangepeel defects was 15% or more, significantly increasing compared to otherheat treatment conditions.

In addition, for the S1 to S17 steel grades described in Table 1, thecalculated values according to equations (1) to (4), permeability, and σphase fraction were measured and are shown in Table 3 below.

TABLE 3 measured measured δ-ferrite σ phase equation fraction equationpermeability equation equation fraction (1) (%) (2) (μ) (3) (4) (%)Inventive 1 S2 4.8 0 −11.9 1.003 20.2 19.9 0.06 Example 2 S3 3.9 0 −7.01.004 22.1 22.0 0.11 3 S5 4.5 0 −10.4 1.003 20.5 20.0 0.16 4 4.5 0 −10.41.004 20.5 20.0 0.08 5 4.5 0 −10.4 1.003 20.5 20.0 0.06 6 4.5 0 −10.41.004 20.5 20.0 0.15 7 S6 0.4 0 −1.7 1.005 28.9 22.1 0.09 8 S7 2.3 0−8.2 1.012 20.4 18.9 0.03 9 S10 1.2 0 −3.4 1.004 28.6 22.1 0.06 10 S111.1 0 −1.5 1.003 27.2 21.9 0.17 11 S12 2.3 0 −7.0 1.006 20.2 19.5 0.0512 S13 2.9 0 −8.4 1.001 20.0 19.8 0.11 Comparative 13 S1 7.7 0 −20.11.001 17.7 17.2 0.03 Example 14 S4 −0.1 0.9 5.2 1.042 25.5 25.7 0.97 15S5 4.5 0 −10.4 1.003 20.5 20.0 0.05 16 4.5 0 −10.4 1.003 20.5 20.0 0.1217 S8 −0.3 0.3 2.5 1.026 34.4 24.1 0.94 18 S9 2.4 0 −10.2 1.002 30.821.6 0.17 19 S14 2.6 0 −9.8 1.002 18.7 19.3 0.03 20 S17 1.8 0 0.0 1.02828.7 24.4 0.84

As shown in Table 3, when the Ni-Ni_(adj) value represented by theequation (1) is positive, it was found that permeability satisfies 1.02μor less, particularly, the examples of the present disclosure satisfy1.012μ or less. When the calculated δ-ferrite fraction according toequation (2) is 0% or less, it was found that the measured δ-ferritefraction was 0%. In addition, when the σ phase formation index is 24 ormore, the σ phase fraction is 0.8% or more, which is close to 1.0%,indicating that the σ phase fraction is significantly increased comparedto other steel types.

Comparative Example 13 did not satisfy the corrosion resistancerequirement due to the low PREN (Eq. (3)) value due to the S1 steelgrade having insufficient Cr content, and the σ phase formation index(Eq. (4)) was also less than 18.

Comparative Example 14 does not satisfy the equations (1) and (2) due tothe S4 steel grade containing excessive Cr, and has a high σ phasefraction, so the permeability was measured to be 1.042μ, and the desirednon-magnetic property of the present disclosure was not satisfied. The σphase formation index also exceeded 24, indicating that the σ phasefraction was close to 1.0%. It was found that the σ phase formation waspromoted by the increase of the Cr content, thereby forming a Crdepletion region.

Comparative Example 17 does not satisfy the equations (1) and (2) due tothe S8 steel grade containing excessive Mo, and has a high σ phasefraction, so the permeability was measured to be 1.026μ, and the desirednon-magnetic property of the present disclosure was not satisfied. The σphase formation index also exceeded 24, indicating that the σ phasefraction was close to 1.0%. It was found that the σ phase formation waspromoted by the increase of the Mo content, thereby forming a Modepletion region. Through this, it was confirmed that when addingadditional Mo, it should be added at 4.0% or less.

Comparative Example 18 did not meet the corrosion resistance requirementdue to the high PREN value due to the S9 steel grade containing Nexcessively.

Comparative Example 19 did not satisfy the corrosion resistancerequirement due to the low PREN value due to the S14 steel gradecontaining excessive Mn, and it was found that corrosion resistance wasnot secured due to inclusion formation due to an increase in the Mncontent.

In Comparative Example 20, the σ phase formation index exceeded 24 dueto the S17 steel containing excessive Si, and the permeability was highas 1.028μ despite satisfying equations (1) and (2) due to the σ phase,which is a magnetic secondary phase. It was confirmed that Si iseffective in improving corrosion resistance, but when it is excessive,it promotes precipitation of intermetallic compounds such as σ phase,thereby lowering corrosion resistance and non-magnetic properties, andthus should be added at 1.0% or less.

While the present disclosure has been particularly described withreference to exemplary embodiments, it should be understood by those ofskilled in the art that various changes in form and details may be madewithout departing from the spirit and scope of the present disclosure.

INDUSTRIAL APPLICABILITY

The austenitic stainless steel according to the present disclosure maybe applied as a non-magnetic component of various electronic devices,and may secure non-magnetic properties without an additional processsuch as heat treatment for a long time.

1. A non-magnetic austenitic stainless steel with excellent corrosionresistance, the austenitic stainless steel comprising, in percent (%) byweight of the entire composition, C: 0.05% or less, Si: 1.0% or less,Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% or less, theremainder of iron (Fe) and other inevitable impurities, and wherein theaustenitic stainless steel satisfies a following equation (1), and has apermeability of 1.02μ or less.Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1) (Ni,C, Si, Mn, Cr, Mo, Cu, N mean the content (% by weight) of each element)2. The austenitic stainless steel of claim 1, further comprising: inpercent (%) by weight, Cu: 3.0% or less.
 3. The austenitic stainlesssteel of claim 1, further comprising: in percent (%) by weight, Mo: 4.0%or less.
 4. The austenitic stainless steel of claim 1, furthercomprising: in percent (%) by weight, B: less than 0.01%.
 5. Theaustenitic stainless steel of claim 1, wherein the stainless steelsatisfies a calculated δ-ferrite fraction represented by the followingequation (2) of 0% or less.161*{[Cr+Mo+1.5*Si+18]/[Ni+30*(C+N)+0.5*(Cu+Mn)+36]+0.262}−161  (2) (Cr,Mo, Si, Ni, C, N, Cu, Mn mean the content (% by weight) of each element)6. The austenitic stainless steel of claim 1, wherein the stainlesssteel satisfies a pitting resistance equivalent number (PREN)represented by the following equation (3) of the range of 20 to 30.Cr+3.3*Mo+30*N−Mn+Si  (3) (Cr, Mo, N, Mn, Si mean the content (% byweight) of each element)
 7. The austenitic stainless steel of claim 1,wherein the stainless steel satisfies a σ phase formation indexrepresented by the following equation (4) of the range of 18 to 24.Cr+Mo+3*Si  (4) (Cr, Mo, Si mean the content (% by weight) of eachelement)
 8. The austenitic stainless steel of claim 1, wherein thestainless steel has a permeability of 1.012μ or less.
 9. The austeniticstainless steel of claim 1, wherein an average grain size of thestainless steel is 1.012μ or less.
 10. A manufacturing method of anon-magnetic austenitic stainless steel with excellent corrosionresistance, the manufacturing method comprising: hot rolling the slabcomprising, in percent (%) by weight of the entire composition, C: 0.05%or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to16%, N: 0.2% or less, the remainder of iron (Fe) and other inevitableimpurities and satisfying a σ phase formation index represented by thefollowing equation (4) of the range of 18 to 24; and performing asolution heat treatment of the hot rolled material.Cr+Mo+3*Si  (4) (Cr, Mo, Si mean the content (% by weight) of eachelement)
 11. The manufacturing method of claim 10, wherein the slabsatisfies a following equation (1), and satisfies a calculated δ-ferritefraction represented by a following equation (2) of 0% or less.Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)161*{[Cr+Mo+1.5*Si+18]/[Ni+30*(C+N)+0.5*(Cu+Mn)+36]+0.262}−161  (2) (Ni,C, Si, Mn, Cr, Mo, Cu, N mean the content (% by weight) of eachelement).
 12. The manufacturing method of claim 10, wherein the solutionheat treatment is performed at 1,100 to 1,150° C. for 60 to 120 seconds.